Nutplates are small metal plates which are frequently utilized in the fabrication of airframes as fastener components for structural members. They are available in a wide variety of sizes and configurations to suit a broad range of applications. Commonly they have three holes, one threaded ("primary") hole and two ("secondary") unthreaded holes. In use a nutplate is fastened to the back of a structural member by rivets which are engaged in the two secondary holes. Threaded fasteners passing through other structural members and engaging the primary hole in the nutplate are used to fasten structural members together.
Currently, the pattern of holes required to fasten a nutplate to the back of a structural member .degree. is drilled utilizing a two step process. First, a "primary" hole corresponding to the primary hole in the nutplate is drilled through the attaching member (i.e. the structural member or "workpiece", to which the nutplate will ultimately be fastened) using an ordinary drill gun. Then a dual bit drill gun is used to drill two "secondary" holes in the attaching member, corresponding to the two secondary holes in the nutplate. A guide stud protruding from the front of the dual-bit drill gun is engaged into the primary hole of the attaching member to properly orient the secondary holes to be drilled through the attaching member in relation to the primary hole of the attaching member.
In the dual-bit drill gun, the positions of the drill bits relative to one another ("secondary spacing") and to the guide stud ("primary spacing") is determined by the "drillhead". The drillhead contains rotatable shafts adapted to couple to motor driven flexible drive shafts at one end, and to hold drill bits at the other end. The drillhead is specifically fabricated for a particular nutplate configuration. This requires that there be available a separate drillhead for each nutplate configuration, which requires that the drill be removed from use to change the drillhead whenever a new hole pattern is required. Common configurations of nutplates include the "single wing" (wherein the secondary holes are colinear with and offset to one side of the primary hole), "double wing" (wherein the secondary holes are colinear with and on opposite sides of the primary hole), and so-called "Mickey Mouse" (wherein the two secondary holes are noncolinear with respect to the primary hole.